Systems and methods for reducing total dissolved solids (tds) in wastewater by an algal biofilm treatment

ABSTRACT

A system for reducing total dissolved solids in wastewater can include a vertical reactor that can include a flexible sheet material, where the flexible sheet material can be configured to facilitate the growth and attachment of an algal biofilm. The vertical reactor can include a shaft, where the shaft can be associated with and can support the flexible sheet material, and a drive motor, where the drive motor can be coupled with the shaft such that the flexible sheet material can be selectively actuated. The system can include a fluid reservoir containing a portion of wastewater through which the flexible sheet material is configured to pass as well as a stressor operably configured to stimulate the algae to produce an extracellular polymeric substance. A method of reducing total dissolved solids in wastewater includes moving an algal biofilm through the wastewater and moving the algal biofilm through a gas.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/748,211, filed Jan. 21, 2020 which claims thepriority benefit of U.S. provisional patent application Ser. No.62/795,122, filed Jan. 22, 2019, and hereby incorporates the sameapplication herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the technology relate, in general, to biofilm technology,and in particular to the application of a revolving algal biofilmphotobioreactor (RABP) for removal of Total Dissolved Solids (TDS).

BACKGROUND

Total dissolved solids (TDS) is generally comprised of inorganic salts(e.g., chloride, calcium, magnesium, potassium, sodium, bicarbonates,and sulfates) and organic matters dissolved in water. Naturalwaterbodies commonly contain a certain level of TDS, but humanactivities such as agriculture, water use and treatment, urbanization,de-icing salt applications, and mining can significantly exacerbate theTDS level in surface and ground waters. This excess TDS can be toxic toaquatic life. In the U.S., TDS discharge limit for wastewater has beenincreasingly implemented at state levels. Various methods such asreverse osmosis (RO), distillation, and membrane filtration have beendeveloped to reduce/remove TDS from various water streams. However, mostexisting methods are not cost-effective and/or environmental friendly.For example, distillation can produce low conductivity water but theprocess is very energy-intensive due to the large amount of latent heatrequired. A need exists for improved methods of TDS removal that arecost-effective and environmentally friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily understood from a detaileddescription of some example embodiments taken in conjunction with thefollowing figures:

FIG. 1 depicts a flow chart illustrating the methodology generallyassociated with algae harvesting.

FIG. 2 depicts a top view of microalgae being grown on polystyrene foam.

FIG. 3 depicts a partial cutaway perspective view of a revolving algalbiofilm photobioreactor according to one embodiment.

FIG. 4 depicts a schematic front view of the revolving algal biofilmphotobioreactor illustrated in FIG. 3 .

FIG. 5 depicts a top view of microalgae being grown on a variety ofmaterials.

FIG. 6 depicts a bar chart of harvesting frequencies for an algal strainaccording to one embodiment.

FIG. 7 depicts a partial cutaway perspective view of the revolving algalbiofilm bioreactor illustrated in FIG. 3 , shown with grow lights and agas input.

FIG. 8 depicts a partial exploded view of the revolving algal biofilmbioreactor shown in FIG. 3 .

FIG. 9 depicts a perspective view of a revolving algal biofilmbioreactor having a plurality of associated algal growth systems and araceway according to one embodiment.

FIG. 10 depicts a perspective view of the algal growth systemillustrated in FIG. 12 .

FIG. 11 depicts a perspective view of the raceway illustrated in FIG. 12.

FIG. 12 depicts a perspective view of a revolving algal biofilmbioreactor having a plurality of associated algal growth systems and araceway according to an alternate embodiment.

FIG. 13 depicts a perspective view of the algal growth systemillustrated in FIG. 12 .

FIG. 14 depicts a perspective view of a revolving algal biofilmbioreactor having an associated algal growth system and a trough systemaccording to one embodiment.

FIG. 15 depicts a perspective view of the algal growth systemillustrated in FIG. 14 .

FIG. 16 depicts a perspective view of the trough system illustrated inFIG. 14 .

FIG. 17 depicts a perspective view of an algal growth system shown witha harvesting system according to one embodiment.

FIG. 18 depicts a perspective view of an algal growth system accordingto one embodiment.

FIG. 19 depicts a perspective view of a photobioreactor according to oneembodiment.

FIG. 20 depicts a flow chart showing a method for growing and harvestingalgae using a raceway according to one embodiment.

FIG. 21 depicts a flow chart showing a method for growing and harvestingalgae using a trough according to one embodiment.

FIG. 22 depicts a graph of biomass concentration of polyculture each dayin bubble column reactors fed with the following wastewater (WW)sources: low-TDS industrial WW (∘); high-TDS industrial WW (•); Ames WW(▴); and Ames WW+NaCl (Δ).

FIGS. 23A-23D depict the concentration of TDS in the influent andeffluent during the continuous operation of the RAB and BC reactors fedwith the following wastewater (WW) sources: low-TDS industrial WW (FIG.23A); high-TDS industrial WW (FIG. 23B); Ames WW (FIG. 23C); and AmesWW+NaCl (FIG. 23D).

FIGS. 24A-24D depict the concentration of chloride in the influent andeffluent during the continuous operation of the RAB and BC reactors fedwith the following wastewater (WW) sources: low-TDS industrial WW (FIG.24A); high-TDS industrial WW (FIG. 24B); Ames WW (FIG. 24C); and AmesWW+NaCl (FIG. 24D).

FIGS. 25A-25D depict the concentrations of sodium, potassium, calcium,magnesium, and sulfur in the influent and effluent of the continuousoperation of RAB and BC reactors fed with the following wastewater (WW)sources: low-TDS industrial WW (FIG. 25A); high-TDS industrial WW (FIG.25B); Ames WW (FIG. 25C); and Ames WW+NaCl (FIG. 25D).

SUMMARY

A method of reducing total dissolved solids (TDS) in wastewater caninclude providing an algal biofilm, the algal biofilm comprising amaterial configured for the growth and attachment of algae, providing afluid reservoir containing a portion of wastewater fluid, and moving thealgal biofilm through the portion of wastewater fluid in the fluidreservoir. The method can further include providing a stressor to algaein the algal biofilm to stimulate production of an extracellularpolymeric substance and removing a portion of total dissolved solids inthe portion of wastewater fluid with the extracellular polymericsubstance.

An algal growth system for reducing total dissolved solids (TDS) inwastewater can include a vertical reactor comprising a flexible sheetmaterial, the flexible sheet material being configured to facilitate thegrowth and attachment of an algal biofilm, a shaft, wherein the shaft isassociated with and supports the flexible sheet material, and a drivemotor, the drive motor being coupled with the shaft such that theflexible sheet material is selectively actuated. The system can alsoinclude a fluid reservoir, the fluid reservoir containing a portion ofwastewater containing an amount of total dissolved solids, wherein theflexible sheet material is configured to pass through the fluidreservoir during operation of the algal growth system, and a stressor,wherein the stressor is operably configured to stimulate algae in thealgal biofilm to produce an extracellular polymeric substance.

A method of reducing total dissolved solids (TDS) in wastewater caninclude providing an algal growth system comprising a vertical reactorcomprising a flexible sheet material, the flexible sheet material beingconfigured to facilitate the growth and attachment of algae, a shaft,wherein the shaft is associated with and supports the flexible sheetmaterial, and a drive motor, the drive motor being coupled with theshaft such that the flexible sheet material is selectively actuated. Thesystem can also include a fluid reservoir, wherein the flexible sheetmaterial is configured to pass through the fluid reservoir duringoperation of the algal growth system, the vertical reactor beingpositioned at least partially within the fluid reservoir, and a portionof wastewater, wherein the portion of wastewater is retained within thefluid reservoir and includes an amount of total dissolved solids. Themethod can further include rotating the flexible sheet material of thealgal growth system through the portion of wastewater retained in thefluid reservoir in a first liquid phase, rotating the flexible sheetmaterial of the algal growth system through a gas in a second gas phaseto stimulate production of an extracellular polymeric substance, andharvesting the algae from the flexible sheet material. Stimulating theproduction of the extracellular polymeric substance reduces the amountof total dissolved solids in the portion of wastewater.

DETAILED DESCRIPTION

Various non-limiting embodiments of the present disclosure will now bedescribed to provide an overall understanding of the principles of thestructure, function, and use of the systems and processes disclosedherein. One or more examples of these non-limiting embodiments areillustrated in the accompanying drawings. Those of ordinary skill in theart will understand that systems and methods specifically describedherein and illustrated in the accompanying drawings are non-limitingembodiments. The features illustrated or described in connection withone non-limiting embodiment may be combined with the features of othernon-limiting embodiments. Such modifications and variations are intendedto be included within the scope of the present disclosure.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “some example embodiments,” “one exampleembodiment,” or “an embodiment” means that a particular feature,structure, or characteristic described in connection with any embodimentis included in at least one embodiment. Thus, appearances of the phrases“in various embodiments,” “in some embodiments,” “in one embodiment,”“some example embodiments,” “one example embodiment,” or “in anembodiment” in places throughout the specification are not necessarilyall referring to the same embodiment. Furthermore, the particularfeatures, structures or characteristics may be combined in any suitablemanner in one or more embodiments.

Traditionally, algae are grown in open raceway ponds or enclosedphotobioreactors, where algae cells are in suspension and are harvestedthrough sedimentation, filtration, or centrifugation. Due to the lightpenetration problem caused by mutual shading of suspended algal cells,the algal growth in suspension is often limited by light availability.Also, due to the small size (3-30 μm) of algae cells and the dilutealgae concentration (<1% w/v), gravity sedimentation of suspended cellsoften takes a long time in a large footprint settling pond. Filtrationof algal cells from the culture broth can result in filter fouling.Centrifugation can achieve high harvest efficiency; however, the capitalinvestment and operational cost for a centrifugation system can beprohibitively expensive. Due to these drawbacks, an alternative methodfor growing and harvesting algae biomass may be advantageous.

Described herein are example embodiments of revolving algal biofilmphotobioreactor systems and methods that can enhance cell growth andsimplify biomass harvesting. In one example embodiment, systems andmethods can provide cost effective harvesting of algae biomass. In someembodiments, systems and methods can be used to produce algae forbiofuel feedstock, and aquacultural feed, and nutraceuticals. In someembodiments, algal cells can be attached to a material that can berotated between a nutrient-rich liquid phase and a gaseous phase, suchas a carbon dioxide rich gaseous phase, such that alternative absorptionof nutrients and the gas can occur. The algal cells can be harvested byscraping from the surface to which they are attached, which caneliminate harvest procedures commonly used in suspension cultivationsystems, such as sedimentation, flocculation, floatation, and/orcentrifugation. It will be appreciated that systems and methodsdescribed herein can be combined with sedimentation, centrifugation, orany other suitable processes.

The examples discussed herein are examples only and are provided toassist in the explanation of the apparatuses, devices, systems andmethods described herein. None of the features or components shown inthe drawings or discussed below should be taken as mandatory for anyspecific implementation of any of the apparatuses, devices, systems ormethods unless specifically designated as mandatory. For ease of readingand clarity, certain components, modules, or methods may be describedsolely in connection with a specific figure. Any failure to specificallydescribe a combination or sub-combination of components should not beunderstood as an indication that any combination or sub-combination isnot possible. Also, for any methods described, regardless of whether themethod is described in conjunction with a flow diagram, it should beunderstood that unless otherwise specified or required by context, anyexplicit or implicit ordering of steps performed in the execution of amethod does not imply that those steps must be performed in the orderpresented but instead may be performed in a different order or inparallel.

Example embodiments described herein can mitigate air and waterpollution while delivering high value bio-based products such asbio-fuels, nutraceuticals, and animal feeds from microalgae. Exampleembodiments of RAB technology can play a beneficial role in creating analgal culture system that can economically produce algae biomass for,for example, biofuels, nutraceuticals, and animal feeds. Microalgae mayhave a significant impact in the renewable transportation fuels sector.Example embodiments can grow microalgae that can be used in biofuelproduction with a low harvest cost. Algae, if produced economically, mayalso serve as a primary feed source for nutraceuticals and aqua feedsproduction.

Referring to FIG. 1 , low biomass productivity and high cost of algaeproduction can still be the major limitation in industrial scaleoperation. Example embodiments described herein may minimize such costsassociated with the growth and harvesting of algal cells from an aqueousculture system.

Generally, research on algae cultivation is done using suspended algaeculture. This culture method can have drawbacks including low biomassyield and productivity and low efficiency of harvesting the algal cellsfrom liquid culture medium. Example embodiments described herein canpromote a fast cell growth and a simple economical harvesting methodthat may be an improvement over existing methods. Example embodimentscan include an algal growth system or mechanized harvesting system,which can remove concentrated algae in-situ from an attachment materialand can minimize the amount of de-watering needed post-harvest. Exampleembodiments can optimize gas mass transfer due to the algae cells comingin direct contact with, for example, gaseous carbon dioxide when thealgae are rotated through the open air. In an alternate embodiment, thealgae can be rotated within an enclosed structure with natural orartificial grow lighting (e.g., LEDs). For example, the algae can berotated within an enclosed greenhouse 40 (FIGS. 3 and 4 ) having anincreased carbon dioxide concentration relative to the atmosphere, whichmay improve the growth rate of the algae. Example embodiments canutilize minimal growth medium, where the triangular or vertical designin example embodiments may reduce the total water needed for the growthand the chemical costs of growth medium. In one embodiment, suchadvantages may be accomplished by submerging only the lowest portion ofa bioreactor, supporting material, algal growth system, or mechanizedharvesting system into the medium.

Referring to FIG. 2 , microalgae can be grown on the surface ofpolystyrene foam. FIG. 2 illustrates how algae can be harvested byscraping the surface of the foam. The mechanical separation throughscraping of biomass from the attached materials can result in biomasswith water content similar to centrifuged samples (e.g., 80-95% watercontent) and the residual biomass left on the surface can serve as anideal inoculum for subsequent growth cycles.

Referring to FIGS. 3, 4, 7, and 8 , an example embodiment of a revolvingalgal biofilm photobioreactor (RAB) 10, in which algal cells 18 can beattached to a solid surface of a supporting material 12, is disclosed.The photobioreactor 10 can keep the algal cells 18 fixed in one placeand can bring nutrients to the cells, rather than suspend the algae in aculture medium. As shown in FIGS. 3 and 4 , algal cells can be attachedto the supporting material 12 that is rotating between a nutrient-richliquid phase 15 and a CO₂-rich gaseous phase 16 for alternativeabsorption of nutrients and carbon dioxide. The algal biomass can beharvested by scraping the biomass from the attached surface with aharvesting scraper, such as squeegee 20 (FIG. 4 ), or other suitabledevice or system. In example embodiments, the naturally concentratedbiofilm can be in-situ harvested during the culture process, rather thanusing an additional sedimentation or flocculation step for harvesting,for example. The culture can enhance the mass transfer by directlycontacting algal cells with CO₂ molecules in gaseous phase, wheretraditional suspended culture systems may have to rely on the diffusionof CO₂ molecules from gaseous phase to the liquid phase, which may belimited by low gas-liquid mass transfer rate. Example embodiments mayonly need a small amount of water by submerging the bottom of thetriangle-shaped algal growth system or mechanized harvesting system 22in contacting liquid 14 while maximizing surface area for algae toattach. Example embodiments can be scaled up to an industrial scalebecause the system may have a simple structure and can be retrofit onexisting raceway pond systems. Example embodiments can be used in freshwater systems and can be adapted to saltwater culture systems. Forexample, embodiments of this system can be placed in the open oceaninstead of in a raceway pond reactor. In this example application, theocean can naturally supply the algae with sufficient sunlight, nutrient,water, and CO₂, which in turn may decrease operational costs. Referringto FIG. 7 , a gas input 43 and grow lights 42 having any suitablewavelength can be provided in the system.

Still referring to FIGS. 3, 4, 7, and 8 , embodiments of the system caninclude a drive motor 24 and a gear system 26 that can rotate one or aplurality of drive shafts 28, where the one or a plurality of driveshafts 28 can correspondingly rotate the supporting material 12, such asa flexible sheet material. The supporting material 12 can be rotatedinto contact with the contacting liquid 14, which can allow the algalcells 18 to attach to the supporting material 12. The drive motor 24 caninclude a gear system 26 or pulley system that can drive the one or aplurality of drive shafts 28, where the one or a plurality of driveshafts 28 can rotate the supporting material 12 in and out of acontacting liquid 14, for example. Embodiments can also include a liquidreservoir 30, mister, water dripper, or any other suitable component ormechanism that can keep algae, which can be attached to the supportmaterial 12, moist. Embodiments can include any suitable scrapingsystem, vacuum system or mechanism for harvesting the algal cells 18from the supporting material 12. It will be appreciated that the systemcan include one or a plurality of rollers (not shown) that can be guideand support the supporting material 112 in addition to the one or aplurality of drive shafts 28.

In an example embodiment, a generally triangle-shaped mechanizedharvesting system 22 can be provided. Such a configuration can bebeneficial in maximizing the amount of sunlight or light that algalcells 18 are exposed to. However versions of the system can be designed,for example, in any configuration that includes a “sunlight capture”part 32 which can be exposed to air and sunlight, and a “nutrientcapture” part 34 which can be submerged into a nutrient solution orcontacting liquid 14. It will be appreciated that, in a first position,the supporting material 12 can have a portion that is in the “sunlightcapture” part 32 and a portion that is in the “nutrient capture” part34, where rotation of the supporting material 12 to a second positioncan result in different regions corresponding to the “sunlight capture”part 32 and “nutrient capture” part 34. Such movement of the supportingmaterial 12 can, for example, beneficially transition algal cells 18from a nutrient rich liquid to a region with sunlight and a carbondioxide content higher than the outside atmosphere. As will be shown inmore detail herein, a substantially vertical design is contemplated,which may be the simplest and most cost efficient design because such asystem may minimize the amount of wasted space and may maximize theamount of algae produced in a small area by growing this systemvertically. Alternative designs can include a straight vertical reactor,a reactor that is straight but slightly angled to provide more surfacearea for sunlight to hit, a cylindrical reactor, or a square shapedreactor.

Referring to FIG. 8 , the generally triangle-shaped algal growth andmechanized harvesting system 22 can include a supporting material 12that is movable or removable relative to the liquid reservoir 30. Thesupporting material 12, and any associated components such as the one ora plurality of drive shafts 28 and gear system 26, can be movable orremovable for cleaning, replacement, harvesting, adjustment, or thelike. It will be appreciated that such movement can be manual or can beautomated if desirable. In an example embodiment, the liquid reservoir30 can contain a contacting liquid 14 having a first chemical or fluidmakeup, where the supporting material 12 can be lifted or otherwisetransitioned from the liquid reservoir 30 into a second liquid reservoir(not shown) having a second liquid (not shown) having a differentchemical or fluid makeup from the contacting liquid 14. In this manner,the supporting material 12 retaining algal cells 18 can be dipped ortransitioned into a variety of fluids or materials that may maximizealgal growth or otherwise provide a benefit. Such a system can berepeated or adjusted as appropriate. In an alternate embodiment, thesupporting material can be lifted or moved from the liquid reservoir 30and transitioned to a harvesting station. In one embodiment, harvestingcan take place while the supporting material 12 is positioned within theliquid reservoir 30.

Still referring to FIG. 8 , the liquid reservoir 30 can include a pump38 or any other suitable actuator or fluid control. The pump 38 cancirculate the contacting liquid 14, which may improve the growth ofalgal cells 18 and the efficiency of the overall system. It will beappreciated that the pump 38 can be an electric pump, a wheel, apaddlewheel, or can have any other suitable configuration to create anydesirable flow pattern. It will be appreciated that the pump 38 canheat, cool, or otherwise adjust the conditions associated with thecontacting liquid 14. The pump 38 can also be configured for thedelivery of supplemental nutrients, such as supplemental fluidsdelivered at pre-specified times, where such delivery can be manual orautomated. It will be appreciated that the pump 38, and any othersuitable components, can be associated with a computer, controller, ormicrocontroller that can be programmed to provide any suitable automatedfunctionality.

Referring to FIG. 5 , any suitable supporting material 12, such as anysuitable flexible fabric, can be used with the systems and methodsdescribed herein to grow any suitable material. The supporting material12 may include one or more natural materials, one or more syntheticmaterials, or a combination thereof. For example, the microalgaChlorella, such as Chlorella vulgaris can be grown on materials such as,muslin cheesecloth, aramid fiberglass, porous PTFE coated fiberglass,chamois, vermiculite, microfiber, synthetic chamois, fiberglass, burlap,cotton duct, velvet, TYVEK, poly-lactic acid, abrased poly-lactic acid,vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen,cashmere, leather, silk, lyocell, hemp fabric, SPANDEX, polyurethane,olefin fiber, polylactide, LUREX®, carbon fiber, and combinationsthereof. The supporting material or associated material can includerubbers such as, for example, buna-n rubber, butyl rubber, ECH rubber,EPDM rubber, gum rubber, polyethylene rubber, latex rubber, neoprenerubber, polyurethane, SANTOPRENE rubber, SBR rubber, silicone rubber,vinyl rubber, VITON fluoroelastomer, aflas, fluorosilicone, orcombinations thereof. The supporting material or associated material caninclude plastics such as, for example, PETG, acrylic, cast acrylic,polycarbonate, LDPE, PLA, PVC, ABS, polystyrene, HDPE, polypropylene,UHMW, delrin, acetal resin, nylon, cast nylon, CPVC, REXOLITEpolystyrene, NORYL PPO, polyester, PVDF, polysulfone, RADEL PPSU, ULTEMPEI, FEP, PPS, PEEK, PFA, TORLON PAI, TEFLON PTFE, polyimide, antistaticpolycarbonate, antistatic cast acrylic, conductive ABS/PVC, antistaticacetal, atatic-dissipative UHMW, conductive UHMW, antistatic PTFE,glass-filled polycarbonate, strengthened acrylic, strengthened PVC,glass-filled nylon, glass-filled acetal, glass-filled UHMW, glass-filledPTFE, and combinations thereof. The supporting material and associatedmaterials can include metals such as, for example, aluminum, steel, castiron, tungsten carbide, tungsten alloy, stainless steel, nickel,titanium, copper, brass, bronze, lead, tin, zinc, casting alloys, orcombinations thereof. Any suitable material for the supporting materialand associated materials is contemplated including ceramic, felt,fiberglass, foam, foam rubber, foam plastic, glass, leathers, carbonfiber, wire cloth, cellulose, cellulosic or hemicellulosic materialsfrom agricultural by-products, or the like, as well as combinationsthereof.

The material associated with the supporting material 12 can have a highsurface roughness, high hydrophobicity, and high positive surface chargein one embodiment. It will be appreciated that any suitable texture,surface treatment, hybrid material, or the like is contemplated. Thesupporting material, belt, sheet, or band can be altered, modified, orchanged with heat, abrasion, applying another material, chemicallytreating, applying a charged molecule, applying a polar molecule, orcombinations thereof. Referring to FIG. 18 , in one embodiment of analgal growth system 522, the supporting material 512 can including oneor a plurality of ribs 596, can be finned, or otherwise textured suchthat a pump is not needed to agitate an associated contacting liquid,where rotation of the textured supporting material can sufficientlyagitate or otherwise create a desirable fluid dynamic. The algal growthsystem 522 can also include an integrated paddle 598 that can bepositioned within a contacting liquid such that rotation of thesupporting material 512 correspondingly can rotate the integrated paddle598. In alternate embodiments, the supporting material can includeflexible regions and rigid regions, can be a hinged belt, can haveremovable sections, or can otherwise be suitably configured. Forexample, in one embodiment, strips of material can be attached to arotating belt with a hook and loop fastener, where such strips can bepulled off of the rotating belt during harvesting and replaced whenharvesting is complete.

The supporting material 12 can be reinforced by attaching a highstrength and slowly degradable second layer of material to a cell growthmaterial. The photobioreactor 10 can be configured such that the highstrength material comes in contact with components such as rollers,drive shafts, and the like. Such a configuration may help avoid thewearing off of the cell growth material during operation of thephotobioreactor 10. Suitable materials can include materials that arenot easily degraded by water and microbes such as plastic, rubber,TYVEK®, or other slowly degrading materials. Additionally, materials,adhesives, chemicals, or the like can be sprayed onto or otherwiseprovided on the supporting material 12 to facilitate algal attachment.It will be appreciated that any suitable number of layers of material iscontemplated.

It will be appreciated that any suitable algal cells 18 (includingcyanobacteria) as well as fungal strains, such as strains that can beused in aquaculture feed, animal feed, nutraceuticals, or biofuelproduction can be used. Such strains can include Nannochloropsis sp.,which can be used for both biofuel production and aquacultural feed,Scenedesmus sp., a green microalga that can be used in wastewatertreatment as well as for fuel production feedstock, Haematococcus sp,which can produce a high level of astaxanthin, Botryococcus sp. a greenmicroalga with high oil content, Spirulina sp. a blue-green alga withhigh protein content, Dunaliella sp. a green microalga containing alarge amount of carotenoids, the microalga Chlorella, such as Chlorellavulgaris, and/or other microalgae, such as one or more of a group ofmicroalgae species producing a high level of long chain polyunsaturatedfatty acids can include Arthrospira, Porphyridium, Phaeodactylum,Nitzschia, Crypthecodinium and Schizochytrium. Any suitable parameter,including gaseous phase CO₂ concentration, harvesting frequency, therotation speed of the RAB reactor, the depth of the biofilm harvested,the ratio of submerged portion to the air-exposure portion of the RABreactor, or the gap between the different modules of the RAB system canbe optimized for any suitable species. It will be appreciated that thelisted genus and species are described by way of example and additionsand combinations are contemplated. It will also be appreciated thatalgal biofilm may include the algal cells as well as EPS, an associatedfungus in the biofilm, associated microbes in the biofilm includingbacteria (e.g., phosphorus accumulating bacteria, etc.), andcombinations thereof.

Referring to FIG. 6 , any harvesting schedule can be used in accordancewith example embodiments described herein. The mechanism of harvestingbiomass from the biofilm can be, for example, scraping, high pressureair, vacuum, or combinations thereof. Biomass productivity may vary byspecies and any suitable harvesting time is contemplated to maximizesuch productivity. For example, as shown in FIG. 6 , of this specificspecies as a function of harvesting time by growing the algae on a RABsystem then harvesting the cells at different durations. As shown inFIG. 6 , for Chlorella the optimal harvest frequency may be every sevendays. In example embodiments, managing other parameters such as CO₂concentration and nutrient loading may also impact algal growthperformance.

Referring to FIGS. 9-11 , shown is an alternate embodiment of arevolving algal biofilm photobioreactor (RABP) 100, in which algal cells118 can be attached to a solid surface of a supporting material 112 thatcan be rotated between a nutrient-rich liquid phase 115 and a CO₂-richgaseous phase 116 for alternative absorption of nutrients and carbondioxide. The algal biomass can be harvested by scraping the biomass fromthe attached surface with a harvesting mechanism (not shown) such as asqueegee, vacuum, reaper, or the like. The photobioreactor 100 mayrequire only a small amount of water for operation, relative to existingmethods, where only the bottom 150 (FIG. 10 ) of an algal growth unit ormechanized harvesting unit 122 may be immersed in a contacting liquid114. The photobioreactor 100 can include one or a plurality ofmechanized harvesting units 122, having frames 123, that can bepositioned in a raceway 130 containing contacting fluid 114. Exampleembodiments can include a large number of mechanized harvesting unitssuch that the photobioreactor can be scaled up to an industrial scale.For example, a single raceway could have 20, 50, 100, or more mechanizedharvesting units. In an example embodiment, the one or a plurality ofmechanized harvesting units 122 can be retrofitted onto existing racewaypond systems. Example embodiments can be used in fresh water systems andcan be also be adapted to saltwater culture systems. In one example, theocean can naturally supply the algal cells with sufficient sunlight,nutrient, water, and CO₂, which in turn may decrease operational costsassociated with operation of a photobioreactor. Embodiments of themechanized harvesting units can be placed, for example, in any suitablefluid retaining location or device. Further, embodiments of thephotobioreactor 100 can be positioned in a fluid reservoir that iseither natural (e.g., rivers, lakes, etc.) or manmade (e.g., concretetanks, etc.).

Embodiments of the photobioreactor 100 can include a drive motor 124 anda gear system 126 that can rotate one or a plurality of drive shafts128, where the one or a plurality of drive shafts 128 cancorrespondingly rotate the supporting material 112, such as a flexiblesheet material for growing algal cells 118. The photobioreactor 100 caninclude one or a plurality of rollers 129 that can support and guide thesupporting material 112. The supporting material 112 can be rotated intocontact with the contacting liquid 114, which can allow the algal cells118 to attach to the supporting material 112. The drive motor 124 caninclude a gear system 126 or pulley system that can drive the one or aplurality of drive shafts 128, where the one or a plurality of driveshafts 128 can rotate the supporting material 112 into and out of thecontacting liquid 114. Embodiments can also include a raceway 130,mister, water dripper, or any other suitable component or mechanism thatcan keep algae, which can be attached to the support material 112,moist. Embodiments can include any suitable scraping system, vacuumsystem or mechanism for harvesting the algal cells 118 from thesupporting material 112. It will be appreciated that the drive motor 124can be associated with a plurality of mechanized harvesting units 122or, in an alternate embodiment, each mechanized harvesting unit can beassociated with an independent motor, gear, and/or drive shaft system.It may be efficient to operate one or more of the mechanized harvestingunits on the same schedule, but it may also be advantageous to operatesome or all of the mechanized harvesting units on different schedules.For example, in one embodiment, a mechanized harvesting unit exposed tonatural light can be associated with a light sensor (not shown) andcontroller (not shown) such that the rotation speed of the supportingmaterial is optimized relative to the available light. In such anexample, mechanized harvesting units in the same facility may havedifferent, or slightly different environmental conditions, whereoperating each mechanized harvesting unit independently maysubstantially optimize the overall system.

The mechanized harvesting unit 122 can have a generally triangle-shapedconfiguration supported by the frame 123. It will be appreciated thatthe frame 123 can be constructed from any suitable material, such asmetal, and can have any suitable configuration. The frame 123 can besubstantially level relative to a flat surface, can be stepped, orotherwise shaped to accommodate an incline or an uneven surface. Theframe 123 can include telescoping components (not shown), such astelescoping legs, which may allow the frame to be used effectively as aretrofit in existing raceways, for example. The frame 123 can bestackable (not shown) or can be coupled in a side-by-side fashion withother frames in an interlocking manner such that a plurality ofmechanized harvesting systems can be connected to form aphotobioreactor. Such a modular system may allow for a few mechanizedharvesting system designs to be used in a wide variety of locations andsituations.

One or a plurality of mechanized harvesting units 122 can be associatedwith the raceway 130 in any suitable manner or configuration. Forexample, each mechanized harvesting unit 122 can be integral with orpermanently affixed to the raceway 130. In an alternate embodiment, eachmechanized harvesting unit 122 can be selectively removable oradjustable relative to the raceway 130, where the mechanized harvestingunit 122 can be removed for cleaning, harvesting, replacement, upgrade,or the like.

Referring to FIG. 11 , the raceway 130 can have any suitable shape orconfiguration. In one example, the raceway 130 can include a motor 138that can be configured to drive a paddlewheel 139. The paddlewheel 139can be configured to create a current or flow within the raceway 130that may facilitate the growth of algal cells 118. It will beappreciated that the raceway, motor, and paddlewheel are shown by way ofexample only, where any suitable mechanism to provide a desirable flowor current in a suitable reservoir is contemplated. The raceway 130 canbe open or otherwise exposed to light such that algae can easily growwithin the raceway 130. The raceway 130 can have a region 141 that canbe exposed to light and may not contain a mechanized harvesting unit,where the region 141 can be used to cultivate or grow a supply of algalcells 118 within the raceway 130. Providing such a region 141, where theregion 141 can have any suitable shape or configuration, may make thesystem self-sustaining and may reduce the likelihood that the systemneeds to be seeded or re-seeded with algal cells.

Referring to FIGS. 12 and 13 , shown is an alternate embodiment of arevolving algal biofilm photobioreactor (RAB) 200, in which algal cells218 can be attached to a solid surface of a supporting material 212 thatcan be rotated between a nutrient-rich liquid phase 215 and a CO₂-richgaseous phase 216 for alternative absorption of nutrients and carbondioxide. The algal biomass can be harvested by scraping the biomass fromthe attached surface with a harvesting mechanism (not shown) such as asqueegee, vacuum, reaper, or the like. The photobioreactor 200 mayrequire only a small amount of water for operation, relative to existingmethods, where only the bottom 250 (FIG. 13 ) of an algal growth unit ormechanized harvesting unit 222 may be immersed in a contacting liquid214. The photobioreactor 200 can include one or a plurality ofmechanized harvesting units 222, having frames 223, which can bepositioned in a raceway 230 containing contacting fluid 214. Exampleembodiments can include a large number of mechanized harvesting unitssuch that the photobioreactor can be scaled up to an industrial scale.For example, a single raceway could have 20, 50, 100, or more mechanizedharvesting units. In an example embodiment, the one or a plurality ofmechanized harvesting units 222 can be retrofitted onto existing racewaypond systems. Embodiments of the mechanized harvesting units can beplaced, for example, in any suitable fluid retaining location or device.

Embodiments of the photobioreactor 200 can include a drive motor 224 anda gear system 226 that can rotate one or a plurality of drive shafts228, where the one or a plurality of drive shafts 228 cancorrespondingly rotate the supporting material 212, such as a flexiblesheet material for growing algal cells 218. The photobioreactor 200 caninclude one or a plurality of rollers 229 that can support and guide thesupporting material 112. The supporting material 212 can be rotated intocontact with the contacting liquid 214, which can allow the algal cells218 to attach to the supporting material 212. The drive motor 224 caninclude a gear system 226 or pulley system that can drive the one or aplurality of drive shafts 228, where the one or a plurality of driveshafts 228 can rotate the supporting material 212 into and out of thecontacting liquid 214. Embodiments can also include a raceway 230,mister, water dripper, or any other suitable component or mechanism thatcan keep algae, which can be attached to the support material 212,moist. Embodiments can include any suitable scraping system, vacuumsystem or mechanism for harvesting the algal cells 218 from thesupporting material 212. It will be appreciated that the drive motor 224can be associated with a plurality of mechanized harvesting units 222or, in an alternate embodiment, each mechanized harvesting unit can beassociated with an independent motor, gear, and/or drive shaft system.It may be efficient to operate one or more of the mechanized harvestingunits on the same schedule, but it may also be advantageous to operatesome or all of the mechanized harvesting units on different schedules.For example, in one embodiment, a mechanized harvesting unit exposed tonatural light can be associated with a light sensor (not shown) andcontroller (not shown) such that the rotation speed of the supportingmaterial is optimized relative to the available light. In such anexample, mechanized harvesting units in the same facility may havedifferent, or slightly different environmental conditions, whereoperating each mechanized harvesting unit independently maysubstantially optimize the overall system.

The mechanized harvesting unit 222 can have a generally wave-shapedconfiguration supported by the frame 223. It will be appreciated thatthe frame 223 can be constructed from any suitable material, such asmetal, and can have any suitable configuration in accordance withembodiments described herein. The supporting material 212 of themechanized harvesting unit can have a substantially wave-shapedconfiguration as best illustrated in FIG. 13 . The supporting material212 can be a contiguous band of material and can be wound about the oneor a plurality of drive shafts 228 or rollers 229 such that any suitableconfiguration is created. It is contemplated that the supportingmaterial can be a long, contiguous band of material having multiplepeaks and valley, as illustrated in FIG. 12 . As illustrated, a portionof the supporting material 212 can also pass along the bottom 250 of themechanized harvesting unit 222. It will be appreciated that a singlelong band and a plurality of bands having any suitable relationship orconfiguration are contemplated. In an example embodiment, the one or aplurality of drive shafts 228 or rollers 229 can be adjusted such thatdifferent configuration can be created using the same frame 223. Such aninterchangeable system may be beneficial in that certain configurationsmay be beneficial to particular species of algal cells. Aninterchangeable system may also allow for different environmentalconditions, uses, or use on a wide range of scales. Any other suitablecomponent, such as a plate 251 can be provided to secure components,such as the rollers 229, in a desired configuration.

Referring to FIGS. 14-16 , shown is an alternate embodiment of arevolving algal biofilm photobioreactor (RAB) 300, in which algal cells318 can be attached to a solid surface of one or a plurality ofsupporting materials 312 that can be rotated between a nutrient-richliquid phase 315 and a CO₂-rich gaseous phase 316 for alternativeabsorption of nutrients and carbon dioxide. The algal biomass can beharvested by scraping the biomass from the attached surface with aharvesting mechanism (not shown) such as a scraper (e.g., a squeegee),vacuum, reaper, or the like. The photobioreactor 300 may require only asmall amount of water for operation, relative to existing methods, whereonly the bottom 350 (FIG. 15 ) of an algal growth unit or mechanizedharvesting unit 322 may be immersed in a contacting liquid 314. Thephotobioreactor 300 can include a frame 323, which can be positioned ina trough system 330 containing contacting fluid 314. Example embodimentscan include a large number of mechanized harvesting units such that thephotobioreactor can be scaled up to an industrial scale. For example, asingle trough system could have 20, 50, 100, or more mechanizedharvesting units or independent supporting material units. In an exampleembodiment, the one or a plurality of mechanized harvesting units 322can be retrofitted onto existing raceway pond systems. Embodiments ofthe mechanized harvesting units can be placed, for example, in anysuitable fluid retaining location or device.

It will be appreciated that the trough system 330 is show by way ofexample only, where any suitable tubing, configuration, or constructionis contemplated. The trough system 330 can have a serpentineconfiguration such that the trough system 330 forms a substantiallyclosed circuit for fluid flow. The trough system 330 can have anysuitable shape, where the trough system 330 can have interchangeableparts such that different configurations can be created by a user. Thetrough system can include any suitable number of apertures 360 andclosed sections 362, where apertures 360 can be configured to accepteach of the one or a plurality of supporting materials 312. In oneembodiment, the apertures 360 can be associated with a closure when notin use. Alternatively, apertures 360 can be used in sunlight or welllighted areas to help facilitate algal growth in the contacting liquid314. The trough system 330 can be associated with a motor 338 andpaddlewheel 339 that can be configured to create a fluid dynamic orcurrent flow in the trough system 330. In one embodiment, one or aplurality of paddlewheels 339, or other actuators, can be positioned inthe apertures 360.

Embodiments of the photobioreactor 300 can include a drive motor 324 anda gear system 326 that can rotate one or a plurality of drive shafts328, where the one or a plurality of drive shafts 328 cancorrespondingly rotate the one or a plurality of supporting materials312, such as a flexible sheet material for growing algal cells 318. Thephotobioreactor 300 can include one or a plurality of rollers that cansupport and guide the one or a plurality of supporting materials 312 or,as illustrated in FIG. 15 , the bottom of each of the one or a pluralityof supporting materials 312 can hang freely in a substantially verticalconfiguration. The one or a plurality of supporting materials 312 can berotated into contact with the contacting liquid 314, which can allow thealgal cells 318 to attach to the one or a plurality of supportingmaterials 312. The drive motor 324 can include a gear system 326 orpulley system that can drive the one or a plurality of drive shafts 328,where the one or a plurality of drive shafts 328 can rotate the one or aplurality of supporting materials 312 into and out of the contactingliquid 314. Embodiments can also include a trough system 330, mister,water dripper, or any other suitable component or mechanism that cankeep algae, which can be attached to the one or a plurality ofsupporting materials 312, moist. Embodiments can include any suitablescraping system, vacuum system or mechanism for harvesting the algalcells 318 from the one or a plurality of supporting materials 312. Itwill be appreciated that the drive motor 324 can be associated with aplurality of mechanized harvesting units 322 or one or a plurality ofsupporting materials 312. In an alternate embodiment, each of the one ora plurality of supporting materials 312 can be associated with anindependent motor, gear, and/or drive shaft system (not shown). It maybe efficient to operate one or more of the one or a plurality ofsupporting materials 312 on the same schedule, but it may also beadvantageous to operate some or all of the one or a plurality ofsupporting materials 312 on different schedules. For example, in oneembodiment, a supporting material exposed to natural light can beassociated with a light sensor (not shown) and controller (not shown)such that the rotation speed of the supporting material is optimizedrelative to the available light. In such an example, one or a pluralityof supporting materials in the same facility may have different, orslightly different environmental conditions, where operating each one ora plurality of supporting materials independently may substantiallyoptimize the overall system.

The mechanized harvesting unit 322 can have a generallyvertically-shaped configuration of one or a plurality of supportingmaterials 312 that can be supported by the frame 323. It will beappreciated that the frame 323 can be constructed from any suitablematerial, such as metal, and can have any suitable configuration inaccordance with embodiments described herein. Each of the one or aplurality of supporting materials 312 can be a contiguous band ofmaterial, strips, ropes, slats, ribbons, plates, scales, overlappingmaterial, or the like, and can be wound about the one or a plurality ofdrive shafts 328 or rollers (not shown) such that any suitableconfiguration can be created. It is contemplated that the supportingmaterial can be a long, contiguous band of material having multiplepeaks and valleys, or can be separate units as illustrated in FIG. 15 .It will be appreciated that a single long band and a plurality of bandshaving any suitable relationship or configuration are contemplated.

Referring to FIG. 17 , an example embodiment of an algal growth systemor mechanized harvesting unit 422 is shown, in which algal cells 418 canbe attached to a solid surface of a supporting material 412. Embodimentsof the mechanized harvesting unit 422 can include a drive motor (notshown), and a gear system 426 that can rotate one or a plurality ofdrive shafts 428, where the one or a plurality of drive shafts 428 cancorrespondingly rotate the supporting material 412, such as a flexiblesheet material. Embodiments of the mechanized harvesting unit 422 caninclude a harvesting system 480 that can include any suitable manual orautomatic harvesting mechanism and/or a harvesting reservoir 482. Theharvesting system 480 can include a vacuum system 484 and a scraper 486for harvesting the algal cells 418 from the supporting material 412. Thescraper 486 can be coupled with a motor 488 and a pulley system oractuator 490 such that the scraper 486 can be selectively engaged withthe supporting material 412. The motor 488 can be associated with acontroller 492 such that the harvesting system 480 can be programmed toscape, harvest, or perform any other suitable function automatically oron a predetermined schedule.

FIG. 20 depicts a flow chart illustrating one example of a method 1000that can be used for growing and/or harvesting algal cells using araceway, such as the raceway 130 shown in FIGS. 9 and 11 . The method1000 can include Culturing Algal Inoculum 1002, which can includeculturing suspended algae in an open pond, raceway, or the like, untilthe algal cell density is between from about 0.05 g/L to about 1.0 g/L.It will be appreciated that any suitable density of any suitable algalcells is contemplated. The method 1000 can include Starting the RAB1004, which can include rotating or actuating the supporting material ofa photobioreactor, algal growth system, mechanized harvesting unit, orthe like, in accordance with versions described herein. The RAB or othersuitable system can be rotated, for example, at a speed ranging fromabout 4 cm/sec to about 10 cm/sec. The RAB can be rotated at from about2 cm/sec to about 6 cm/sec. The RAB can be rotated at about 4 cm/sec.The RAB can be rotated or otherwise actuated at different speeds, whichcan be selectable, preprogrammed, or based on environmental conditions.Starting the RAB 1004 can include rotating the RAB system for anyduration of time such as from about 5 days to about 20 days, whereduration of operation can depend on the speed of the algal cellsattachment on the surface of the RAB materials.

The method 1000 can include Establishing Initial Biofilm 1006, which caninclude the growth of algal cells on the supporting material of an RABor photobioreactor. The initial biofilm can be deemed to be establishedwhen, for example, a threshold density of algal cells is determined.Such a threshold can be any suitable density and the density can bedetermined using any suitable system or method. The method 1000 caninclude Initial Harvesting 1008, which can include harvesting the algalbiomass from the supporting material of the RAB or photobioreactor.Initial Harvesting 1008 can be accomplished by scraping the algalbiofilm, vacuuming, pressurized air, or by any other suitable method.

The method 1000 can include Algae Regrowth 1010, where after harvesting,residual algal cells can remain on the supporting material surface andcan automatically serve as inoculum for a next cycle of growth orregrowth. Harvesting can be performed such that a sufficient density ofalgal cells can be left on the supporting material to facilitateregrowth. Algae Regrowth 1010 can include operating, actuating, orrotating the algal biofilm, RAB, or photobioreactor for any suitabletime period such as from about 3 days to about 8 days. The time foroperating the RAB can depend, for example, on the algal species, cultureconditions, rotating speed of the RAB system, the liquid fluid ratereservoir, or any other suitable factor. Method 1000 can includeRegrowth Harvesting 1012, which can include harvesting the algal biofilmthat has accumulated on the supporting material. The method 1000 caninclude repeating Algae Regrowth 1010 and Regrowth Harvesting 1012 foras many times as appropriate. The system can operate substantiallyindefinitely, or can be periodically interrupted for cleaning or forother reasons. The method 1000 can include Processing Algal Biomass1014, which can include processing the harvested algae by, for example,drying and extracting oil from the harvested algal cells. It will beappreciated that any suitable processing is contemplated.

FIG. 21 depicts a flow chart illustrating one example of a method 1100that can be used for growing and/or harvesting algal cells, such as witha photobioreactor 600 shown in FIG. 19 , a trough, a partially enclosedfluid reservoir, or other suitable bioreactor. In such a system, it maybe beneficial to seed or otherwise provide algal cells grown at a firstlocation 602 (FIG. 19 ) and transport the algal cells via a channel 604(FIG. 19 ), or other suitable connection, to a second location 606 (FIG.19 ), such as to a photobioreactor provided in accordance with versionsdescribed herein. The first location can be fluidly coupled to thesecond location or, in an alternate embodiment, the first location canbe a portable bioreactor that can be selectively connected to the secondlocation as needed.

The method 1100 can include Culturing Algal Inoculum 1102, which caninclude culturing suspended algae in an open pond, portablephotobioreactor, or the like, at the first location until the algal celldensity is between, for example, from about 0.05 g/L to about 3.0 g/L.It will be appreciated that any suitable density of any suitable algalcells is contemplated, although in one embodiment the cell density canbe higher than in an open raceway system, where the reduction of lightin a trough system may benefit from a higher initial cell density. Themethod 1100 can include Circulating Algae 1103, which can includeproviding or otherwise delivering the algal cells from the firstlocation to the trough or partially enclosed system, which can includegenerating a fluid dynamic or flow such that algal cells from the firstgrowth region are transitioned to the trough in the second region. Themethod 1100 can include Starting the RAB 1104, which can includerotating or actuating the supporting material of a photobioreactor,algal growth system, mechanized harvesting unit, or the like, inaccordance with versions described herein. The RAB or other suitablesystem can be rotated, for example, at a speed ranging from about ¼cm/sec to about 10 cm/sec. The RAB can be rotated at from about 2 cm/secto about 6 cm/sec. The RAB can be rotated at about 4 cm/sec. The RAB canbe rotated or otherwise actuated at different speeds, which can beselectable, preprogrammed, or based on environmental conditions.Starting the RAB 1104 can include rotating the RAB system for anyduration of time such as from about 5 days to about 20 days, whereduration of operation can depend on the speed of the algal cellsattachment on the surface of the RAB materials.

The method 1100 can include Establishing Initial Biofilm 1106, which caninclude the growth of algal cells on the supporting material of an RABor photobioreactor. The initial biofilm can be deemed to be establishedwhen, for example, a threshold density of algal cells is determined.Such a threshold can be any suitable density and the density can bedetermined using any suitable system or method. The method 1000 caninclude Initial Harvesting 1108, which can include harvesting the algalbiomass from the supporting material of the RAB or photobioreactor.Initial Harvesting 1008 can be accomplished by scraping the algalbiofilm, vacuuming, pressurized air, or by any other suitable method.

The method 1100 can include Stopping Circulation 1109, which can includestopping delivery of algal cells from the first growth location to thesecond trough location, for example. In one embodiment, once the RAB isseeded with algal cells, the RAB may no longer need to be seeded orotherwise infused with additional algal cells for subsequent regrowthand harvesting steps. It will be appreciated that a feeder or seedingsystem for algal cells can be reattached or can be maintained throughoutif desirable. The method 1100 can include Algae Regrowth 1110, whereafter harvesting, residual algal cells can remain on the supportingmaterial surface and can automatically serve as inoculum for a nextcycle of growth or regrowth. Harvesting can be performed such that asufficient density of algal cells can be left on the supporting materialto facilitate regrowth. Algae Regrowth 1110 can include operating,actuating, or rotating the algal biofilm, RAB, or photobioreactor forany suitable time period such as from about 3 days to about 30 days,about 3 days to about 8 days, or longer than 30 days. The time foroperating the RAB can depend, for example, on the algal species, cultureconditions, rotating speed of the RAB system, the liquid fluid rate ofthe reservoir, the type of reservoir, or any other suitable factor.Method 1100 can include Regrowth Harvesting 1112, which can includeharvesting the algal biofilm that has accumulated on the supportingmaterial. The method 1100 can include repeating Algae Regrowth 1110 andRegrowth Harvesting 1112 for as many times as appropriate. The systemcan operate substantially indefinitely, or can be periodicallyinterrupted for cleaning or for other reasons. The method 1100 caninclude Processing Algal Biomass 1114, which can include processing theharvested algae by, for example, drying and extracting oil from theharvested algal cells. It will be appreciated that any suitableprocessing is contemplated.

Example systems and methods can include developing a biofilm-basedmicroalgae cultivation system (RAB) that could be widely adapted by themicroalgae industry for producing, for example, fuels and high valueproducts, as well as for treating municipal, industrial, andagricultural wastewater. Microalgae use photosynthesis to transformcarbon dioxide and sunlight into energy. This energy is stored in thecell as oil, which has a high energy content. The oil yield from algaecan be significantly higher than that from other oil crops. Algae oilcan generally be easily converted to biodiesel and could replacetraditional petroleum-based diesel. In addition to fuel production,microalgae have also been rigorously researched for the potential toproduce various high value products such as animal feed, omega-3polyunsaturated fatty acids, pigments, and glycoproteins.

Another example application for a biofilm-based microalgae cultivationsystem (RAB) that could be widely adapted by the microalgae industry isfor treating municipal, industrial, and agricultural wastewater.Specifically, systems and methods may include reducing total dissolvedsolids (TDS) in wastewater by an algal biofilm treatment such as byusing a continuous revolving algal biofilm reactor. Total dissolvedsolids (TDS) comprising various inorganic salts (e.g., chloride,calcium, magnesium, potassium, sodium, bicarbonates, and sulfates) andorganic compounds is emerging as toxic pollutants to human and aquaticsystems. Human activities such as agriculture, water use and treatment,urbanization, de-icing salt applications, and mining can significantlyexacerbate the TDS level in surface and ground waters. Compared to theexisting TDS removal methods (e.g., physical adsorption, reverseosmosis, distillation, membrane filtration, and bacteria-basedbioremediation), biological absorption by microalgae is a mild andenvironmental friendly method for TDS removal. Algal cells absorb TDSspecies as nutrients and minerals to support their physiology andmetabolisms while reducing TDS in water.

An example embodiment of a method of reducing TDS in wastewater by analgal biofilm treatment includes inducing the biofilm to produceextracellular polymeric substances (EPS)—a 3-D polymer network tofacilitate algal cells to adhere on the belt and interact eachother—using the revolving algal biofilm system in which an algal biofilmmoves between the wastewater and a gas phase. In particular, thenegatively charged functional groups (e.g., carboxyl, hydroxyl, andphosphoric groups) in the EPS can adsorb various salts and organicmatters. When used to treat wastewater with high TDS content, thepolysaccharides in EPS have a very high binding capacity. Thisphysically-based adsorption, together with the biological assimilationby the biofilm cells, enables the RAB system to remove a wide spectrumof dissolve solids from the wastewater.

The method may include, for example, increasing the EPS production bystressing the algae in the algal biofilm systems. Correspondingly, thesystem may include a stressor that is operably configured to stimulatethe algae to produce an extracellular polymeric substance. In general,EPS is produced as a response to algal cells' defense mechanisms againstabiotic or biotic stresses or is enhanced by manipulations of thestressors. Algae have evolved to grow in water or very damp conditions,and bringing algal cells outside of the water in the revolving algalbiofilm system triggers the defense mechanism to produce EPS to resistdehydration of algal cells. Example stressors include, withoutlimitation, changes in pH (e.g., increasing the pH of the algal biofilm;decreasing the pH of the algal biofilm), changes in temperature (e.g.,increasing the temperature of the algal biofilm; decreasing thetemperature of the algal biofilm; modulating the temperature of thealgal biofilm), exposing the algal biofilm to a gas phase, time spentoutside of the wastewater, ratio of time in wastewater vs. out ofwastewater (i.e., gas vs. liquid phase), adjusting the amount of lightapplied to the algal biofilm (e.g., using a dark cycle), and adjustingthe wavelength of the light applied to the algal biofilm. Additionallyor alternatively, a compound configured to increase the production ofEPS may be added to the biofilm support or to the wastewater itself. Therevolving algal biofilm system can have a height ranging from, forexample, 1-ft to 30-ft tall. The gas/liquid phase ratio can range from,for example, 0.2% (1:500) to 50% (1:2). In an embodiment, the speed ofrotating of the algal biofilm can be from 0.1 cm/sec to 100 cm/sec.

The method may include promoting the selective growth of algae thatproduces a greater amount of EPS. In other words, the EPS productionvaries based on the algae species in the algal biofilm. Green algaspecies for high EPS production include, without limitation, ChlorellaVulgaris, Chlorella ellipsoidea, Chlamydomonas sp., Botryococcusbraunii, and Dunaliella salina.

Additionally, or alternatively, an example embodiment of a method ofreducing TDS in wastewater by an algal biofilm treatment includesprecipitating salts on the algal biofilm or supporting material usingthe RAB system. For example, abiotic salts may precipitate on thesurface of the algal biofilm or supporting material. The system may beadjusted to increase such precipitation. For example, increasing ordecreasing the pH of the wastewater may facilitate precipitation of theions. This chemical precipitation, along with the physically-basedadsorption by EPS and biological assimilation by the biofilm cells,enables the RAB system to remove a wide spectrum of dissolve solids fromthe wastewater.

The following examples are provided to help illustrate the presenttechnology, and are not comprehensive or limiting in any manner.

Example 1

Wastewater Streams. Four types of wastewaters representing industrialeffluents and municipal wastewater were used. These wastewaters include(i) synthetic industrial effluent with low TDS strength (Industry WW/lowTDS), (ii) synthetic industrial effluent with high TDS strength(Industry WW/high TDS), (iii) municipal wastewater (primary effluentafter solids being screened out but before entering the 1stsedimentation basin) from Ames water pollution control plant in Ames,IA, USA (Ames WW), and (iv) Ames WW supplemented with sodium chloride(Ames WW+NaCl). The compositions of those wastewaters and preparationmethods are provided in Table 1.

TABLE 1 Wastewater (WW) sources Low-TDS High-TDS Components IndustrialIndustrial Ames WW + (mg/L) WW WW Ames WW NaCl Sodium 417 1,601 88 425Potassium 64 252 13 13 Calcium 368 1,359 80 79 Magnesium 97 324 17 16Chloride 1,250 4,500 175 781 Sulfur 138 540 33 37 Nitrogen 14 56 26 26Phosphorus 9 36 12 13 Silicon 23 92 Not added Not added BBM trace 10mL/L 10 mL/L Not added Not added metals stock solutions

The Low-TDS industrial WW was prepared by dissolving 1,000 mg/L NaCl,1,000 mg/L CaCl₂, 100 mg/L KNO₃, 500 mg/L MgSO₄, 100 mg/L NaSiO₃, 50mg/L K₂HPO₄ and 10 mL/L Bold's Basal Medium (BBM) trace metal stocksolution into water. The composition of the BBM trace metal stocksolution includes 97 mg/L FeCl₃·6H₂O, 41 mg/L MnCl₂·4H₂O, 5 mg/L ZnCl₂,2 mg/L CoCl₂·6H₂O and 4 mg/L Na₂MoO₄·2H₂O. The High-TDS industrial WWhas the same component species at a concentration of four times theconcentration of those in Low-TDS industrial WW. The Ames WW+NaCl wasprepared by adding 1,000 mg/L sodium chloride into Ames WW.

The Industry WW with high TDS and low TDS were used to mimic industrialeffluents. The salts concentration in these two effluents was preparedbased on data commonly recorded by the Metropolitan Water ReclamationDistrict (MWRD) of Greater Chicago. The Ames WW+NaCl mimicked themunicipal wastewater with high salt content.

Microalgae Seed Cultures. A microalgal seed culture (0.5-1 g/L ofbiomass, dry basis) was maintained at a raceway pond (1,000 L workingvolume) at the Algal Production Facility at Iowa State University inBoone, IA, USA. The culture has been maintained using Bold's BasalMedium (BBM) with half of the raceway pond culture being exchanged withfresh medium every 7 days. The pond has been operated for four years anda stable community containing various green algae, diatom andcyanobacteria species with minimal amount of prokaryotes bacteria andeukaryotic fungus has been established over the year of subculture.

RAB System Design and Operation. A flexible cotton duct canvas belt wasstretched around drive shafts to form a vertical configuration. Thelower region (about 10%) of the belt was submerged in a liquid reservoir(1.2 L working volume) to supply nutrients, while the rest of the beltwas exposed to the air to access light irradiation. The shafts weredriven by a motor at speed of 4 cm/sec to rotate the belt between theliquid and gas phases. To initiate cell attachment on the RAB belt, theliquid reservoir was inoculated with the algal seed culture and the RABbelt was rotated under continuous illumination of 110-120 μmol photonsm−2 s−1 at 25° C. The suspended algal cells gradually attached on theRAB belt over a period of 2-3 weeks, during which the reservoir wassupplemented with additional seed culture to compensate for waterevaporative loss. After initial attachment the algal biomass washarvested by scraping and the residual colonies remained on the materialserved as inoculum for the next growth cycle.

Each wastewater stream was used as the influent to feed the RAB liquidreservoir, with the equal volume of the effluent being discharged. Theeffluent discharge/influent feeding was operated on daily basis with ahydraulic retention time (HRT) of 1 day and 3 days, respectively. Theeffluent discharged from the liquid reservoir was centrifuged at 5,000rpm at 4° C. for 5 min to remove the solid residual; the supernatant wasimmediately analyzed for TDS and chloride concentrations. The remainingsupernatant was stored at −20° C. for further analyzing saltconcentrations. The biomass was harvested by scraping the biofilm fromthe RAB belt every 6 days. The harvested biomass was freeze-dried todetermine the cell dry weight, and then stored for further analysis ofions contents.

Comparative Bubble Column Design and Operation. Suspended cultures onbubble column (BC) reactors were also performed as a comparison baselinefor the RAB system. The BC reactors were made from Pyrex glass with aninner diameter of 6.5 cm and a height of 50 cm. Each column had aworking volume of 1.2 L. The BC reactor was inoculated with 1.2 L seedcultures. The HRT was set at 3 days, i.e., 400 ml of effluent wasdischarged from the reactor and same amount of influent was fed on dailybasis. Modified BBM medium, as described by Orosa et al., “Productionand analysis of secondary carotenoids in green alga,” Journal of AppliedPhycology 12:553-556 (2000), was used as influent to the reactor in thefirst six days of operation to ensure the system reached a steady state;then, the feeding influents were switched to the different wastewatersas described above. During the continuous operation, the optical densityof the cell suspension in the discharged effluent was determined at 680nm (OD₆₈₀) on daily basis and then converted into dry cell weightconcentration based on the linear relationship between OD₆₈₀ and cellconcentration. Then, the effluent discharged from the BCs wascentrifuged to separate cell suspension into supernatant and biomasspellets. The supernatant was stored for analysis of TDS, chloride, andsalt concentrations. The cell pellet was freeze-dried and stored forfurther analysis of ash and ions contents. During the operation, the BCswere aerated with air at 1.0 L/min under continuous illumination of110-120 μm⁻² s⁻¹ light intensity at 25° C.

Determination of TDS, Chloride, and Other Ions Concentrations in Liquid.TDS and chloride concentrations were determined by Multi-ParameterPCSTesr 35 (Oakton, CA, USA) and Chloride Test kits (Hach, CO, USA),respectively. The concentrations of the sodium, potassium, calcium,magnesium, and sulfur were determined by an iCAP 7400 inductivelycoupled plasma-optical emission spectrometry (ICP-OES; ThermoScientific) with the program Qtegra (Version 2.7.2425.65, ThermoScientific). Nitric acid (2%) was used as rinse solution. Yttrium ICPstandard (5 ppm) and IV-ICPMS-71A (Inorganic, USA) were used as theinternal standard and elemental standards, respectively. The wavelengthused for sodium, potassium, calcium, magnesium and sulfur were 589 nm,766 nm, 315 nm, 279 nm, and 180 nm, respectively. The analyticalwavelength was chosen based on EPA-METHOD 6010 C and the elementalstandards.

Determination of Ash and Ion Contents in Biomass. The ash content ofbiomass was determined by heating the biomass at 550° C. for 6 h. Toanalyze the contents of various elements, 5 mL nitric acid were used todigest about 20 mg dry biomass in an Anton-Paar Multiwave GO system witha 30 min-long microwave program (10-min ramp to reach a power of 1200 W,followed with 10-min at 1200 W and 180° C. and then 10-min cooling).Digested samples were diluted with deionized water into 50 mL, whichwere then analyzed for elemental composition using ICP-OES. The biomasscontents of these elements were calculated based on the elementconcentrations in the digested liquid and the biomass dry weight.

Determination of EPS Compositions in Algal Biomass. The biomassharvested from the RAB and BC reactors were rinsed twice with distilledwater and treated with sonication to extract the EPS. The cell pelletwas suspended in 20 ml of phosphate buffer solution (10 mM NaCl, 1.2 mMKH₂PO₄, and 6 mM Na₂HPO₄) at a concentration equivalent to 1 g/L (drybasis). The cell pellet solution was placed in an ice bath and EPS wasextracted with a Model 500 Sonic Dismembrator (Fisher Scientific, USA)at 40% sonication intensity for 2 min. The samples were then centrifugedat 9,000 rpm for 15 min, and the supernatant containing EPS wascollected. The protein and polysaccharide concentrations in thesupernatant solution were determined by Total Protein Kits (Sigma, USA)and based on the method reported by Dubois et al. (1956), respectively.These concentration data (mg/L) were then converted into the cellularcontent of the protein and the polysaccharide (mg/g dry biomass) basedon the volume of the supernatant and the equivalent biomass dry weight.Total EPS content was determined by combining the protein andpolysaccharide contents.

Results. The experimental data were analyzed through one-way ANOVA. TheF value and P values were determined, and a P value of less than 0.05was regarded as significant.

Microalgae Growth and Ash Contact in BC and RAB Reactors. The algalgrowth performance in BC reactors fed with different wastewaters wasevaluated. FIG. 22 shows the daily change of ash-containing biomassdensity in continuous culture over 30 days of operation. All thereactors were fed with BBM medium in the first six days and thenswitched to the different wastewater streams as the influent. The cellgrowth was fluctuated in the first 18-20 days before reaching the quasisteady state. The reactor was operated at 3-day of HRT. The steady statebiomass concentration in High-TDS industrial WW reached around 1,100mg/L, higher than the other three types of wastewaters. The cell growthin the other three wastewaters was similar, without significantdifference.

The biomass productivity (P_(BC)) in BCs was determined as follows,

$\begin{matrix}{P_{BC} = \frac{C}{HRT}} & (1)\end{matrix}$

where C is the biomass concentration (mg/L), and HRT is set at 3 days.Productivities based on ash-containing and ash-free biomass weredetermined. Table 2 shows the productivity and ash content of thebiomass produced from bubble column reactors fed with the differentwastewater sources.

TABLE 2 Ash-containing Ash-free biomass biomass Wastewater productivityAsh content productivity sources (mg DW/L-day) (%) (mg AFDW/L-day)Low-TDS 126 ± 16.66 30.91 ± 3.88 87 ± 11.51 Industrial WW High-TDS 304 ±22.86 65.29 ± 0.94 106 ± 7.94  Industrial WW Ames WW  97 ± 14.71 22.79 ±2.24 75 ± 11.36 Ames WW + 110 ± 16.07 14.79 ± 1.70 94 ± 13.69 NaCl

The industrial WW with high TDS resulted in the highest productivity forboth ash-containing biomass and ash-free biomass. The other three typesof wastewater had similar biomass productivity. The ash content of thebiomass derived from the industrial WW with high TDS was the highest dueto the high salt concentration in this type of wastewater.

The algal growth in RAB reactors fed with different wastewater streamswas also evaluated. The attachment surface based biomass productivitywas determined as follows,

$\begin{matrix}{P_{RAB} = \frac{DW}{B \times F}} & (2)\end{matrix}$

where P_(RAB) is surface based biomass productivity (mg/m²-day), DW isthe dry weight (mg) of biomass harvested from the RAB belt, B is thesurface area of the attachment belt (0.171 m²), and F is the frequencyof harvesting biomass (six days).

The biomass productivity and ash content of the biomass produced fromRAB reactors at 1-day HRT (RAB-1) and RAB at 3-day HRT (RAB-3), fed withdifferent wastewater sources, are shown in Table 3.

TABLE 3 Ash-containing Ash-free biomass biomass productivityproductivity Wastewater (mg DW/m²-day) Ash content (%) (mg AFDW/m²-day)sources RAB-1 RAB-3 RAB-1 RAB-3 RAB-1 RAB-3 Low-TDS  527 ± 3.24 596 ±127 30.58 ± 1.92 25.07 ± 6.62 366 ± 2.25 446 ± 97.0 Industrial WWHigh-TDS 2,549 ± 4.70  2,556 ± 300    61.69 ± 10.52 52.29 ± 0.54 977 ±3.82 1,219 ± 143  Industrial WW Ames WW 623 ± 137 595 ± 131 20.22 ± 3.1214.10 ± 5.44 497 ± 109  511 ± 112  Ames 600 ± 130  553 ± 92.7 21.51 ±6.75 17.18 ± 4.94 471 ± 101  458 ± 92.5 WW + NaCl

Among four different wastewaters, High-TDS industrial WW resulted inash-containing biomass productivities of 2,549 mg/m²-day (1-day HRT) and2,556 mg/m²-day (3-day HRT), about 4 to 5 times higher than those fedwith other types of wastewaters. Considering the high ash content in thebiomass, the ash-free based biomass productivity was also evaluated.Again, High-TDS industrial WW resulted in the highest ash-free biomassproductivities of 977 mg/m²-day (1-day HRT) and 1,219 mg/m²-day (3-dayHRT) among different wastewater streams. Between the two HRT levels,however, the biomass productivity did not vary significantly.

Although the RAB and BC reactors used different criteria to quantify thebiomass productivity, the above results consistently indicated that asimilar trend of algae growth in different types of wastewater streams,i.e., High-TDS industrial WW resulted in the best cell growth while theother three types of wastewater streams led to a similar growthperformance. Compared to the algal productivity obtained in High-TDSindustrial WW, the limited cell growth in low-TDS industrial WW, AmesWW, and Ames WW+NaCl were probably due to the insufficient nutrients,particularly essential nutrients such as nitrogen and phosphorus inthese three wastewater streams (see Table 1).

TDS Removal Performance. The TDS concentrations in the effluent of RABand BC reactors were monitored during the entire continuous operationperiod. FIGS. 23A-23D shows the TDS concentrations in influent andeffluent of RAB and BC reactors at 3-day HRT conditions. The influentTDS concentrations of these reactors maintained constant during thecontinuous operation period, ranging from 840 to 12,000 mg/L. For eachtype of wastewater, the effluent TDS concentrations increased initiallyand reached the steady state with the culture progressing. Overall, theRAB reactors have lower TDS concentrations than the BC reactors.

A summary of the TDS removal performance in RAB and BC reactors ispresented in Table 4. Table 4 shows the TDS removal efficiency (TDS-E,%), the removal rate based on liquid volume (TDS-Rvolume, mg/L-day), andthe removal rate based on surface area (TDS-Rsurface, mg/m2-day) of RABreactor at 1-day HRT (RAB-1), the RAB reactor at 3-day HRT (RAB-3), andthe bubble column reactor at 3-day HRT (BC-3), respectively fed withdifferent wastewater sources.

TABLE 4 TDS removal parameters under different Algal Reactor-HRT WWsources RAB-1 RAB-3 BC-3 TDS-E (%) Low-TDS  9.10 ± 3.26 16.24 ± 8.984.05 ± 0.17 industrial WW High-TDS 23.83 ± 3.59 27.33 ± 5.09 3.37 ± 0.92industrial WW Ames WW 12.39 ± 1.43 25.90 ± 8.03 8.12 ± 2.06 Ames WW + 8.44 ± 1.40 14.35 ± 5.12 2.99 ± 1.51 NaCl TDS-R_(volume) (mg/L-day)Low-TDS   309 ± 38.26   183 ± 23.24 45.73 ± 2.06  industrial WW High-TDS2,783 ± 192  1,089 ± 189   121 ± 11.12 industrial WW Ames WW   101 ±12.83  72.80 ± 23.64 22.40 ± 5.60  Ames WW +   165 ± 17.43  96.37 ±35.20 20.65 ± 14.01 NaCl TDS-R_(surface) (mg/m²-day) Low-TDS 2166 ± 1741,284 ± 100  n/a Industrial WW High-TDS 19,530 ± 1,479  7,642 ± 52.47n/a Industrial WW Ames WW   707 ± 90.06   511 ± 77.18 n/a Ames WW +1,159 ± 385    676 ± 71.46 n/a NaCl

Overall, TDS removal efficiency (TDS-E) of the RAB reactors was higherthan the BC reactors. Among the two HRT levels for the RAB reactors, thelonger HRT resulted in higher TDS-E values. Among four types ofwastewaters, industrial WW with high TDS led in the highest TDS-Evalues. The TDS removal rate by the algal culture systems was alsoevaluated based on the liquid volume (TDS-R_(volume)) and attachmentsurface (TDS-R_(surface)). Similar to the trend of TDS-E, TDS-R_(volume)of the RAB reactors was much higher than that of the BC reactor. Theindustrial WW/high TDS also demonstrated the best TDS removal rate amongfour different wastewaters. However, contrary to that the trend of TDS-Ewith HRT, shorter HRT resulted in higher TDS-R_(volume) andTDS-R_(surface) values for the RAB reactors, probably due to the higherTDS mass turnover rate at shorter HRT.

The results indicate that the RAB system was more effective than thesuspended algae system for removing TDS from wastewater and was capableof decreasing TDS up to 27% at 3-day of HRT by the RBA reactor (Table4). Thus, the RAB system can serve as an efficient and environmentallyfriendly system for TDS removal from wastewater.

Chloride Removal Performance. As chloride is the major ion in all thefour wastewater streams tested, the removal performances of thisspecific TDS species were investigated. The chloride concentrations ininfluent and effluent of the RAB and BC reactors were monitored. Asshown in FIGS. 24A-24D, for all the four wastewater streams, thechloride concentrations in effluent increased initially and reachedsteady state after 10 to 20 days of operation, depending on the types ofthe wastewater and reactors. RAB reactors resulted in a lower chlorideconcentrations in effluent compared to the BC reactor.

The chloride removal performance was further summarized in Table 5.Table 5 shows the chloride removal efficiency (Chloride-E, %), theremoval rate based on liquid volume (Chloride-Rvolume, mg/L-day), andthe removal rate based on surface area (Chloride-Rsurface, mg/m2-day) ofthe RAB reactor at 1-day HRT (RAB-1), the RAB rector at 3-day HRT(RAB-3), and the bubble column reactor at 3-day HRT (BC-3), respectivelyfed with different wastewater sources.

TABLE 5 Chloride removal parameters under Algal Reactor-HRT different WWsources RAB-1 RAB-3 BC-3 Chloride-E (%) Low-TDS Industrial 21.21 ± 8.07 31.61 ± 9.42 13.03 ± 5.71 WW High-TDS Industrial 27.13 ± 12.20  37.32 ±13.19 13.47 ± 5.05 WW Ames WW 15.44 ± 1.33  34.07 ± 8.98 19.42 ± 2.26Ames WW + NaCl 15.74 ± 5.54  35.39 ± 9.82 11.08 ± 1.37Chloride-R_(volume) (mg/L-day) Low-TDS Industrial  262 ± 24.71   133 ±14.25  54.15 ± 24.29 WW High-TDS Industrial 1,215 ± 310    555 ± 63.00  195 ± 54.20 WW Ames WW 26.01 ± 11.31 19.81 ± 2.85 11.07 ± 5.93 AmesWW + NaCl  112 ± 37.36  93.28 ± 17.81 29.08 ± 4.21 Chloride-R_(surface)(mg/m²-day) Low-TDS Industrial 1,842 ± 174   936 ± 100 n/a WW High-TDSIndustrial 8,526 ± 992  3,895 ± 414  n/a WW Ames WW  184 ± 80.02   139 ±20.00 n/a Ames WW + NaCl 786 ± 260   650 ± 70.05 n/a

The trends of the chloride removal performance (removal efficiency andremoval rate) were similar to those observed in the TDS. Both chlorideremoval efficiency and removal rate (volume- and surface-based) of theRAB reactors were higher than those of the BC reactor. Among the two HRTlevels tested for the RAB reactors, shorter HRT resulted a lowerchloride removal efficiency but a much higher removal rate. IndustrialWW with high TDS had the best chloride removal performance than theother three types of wastewaters. The combined results in Tables 4 and 5indicate that the RAB reactor was more effective than the BC reactor forremoving TDS most likely through the predominant chloride.

Removal of Various Ions from Wastewater. In addition to chloride, theremoval of other major ionic components such as sodium, potassium,calcium, magnesium and sulfur (Table 1) from wastewater streams was alsodetermined. The concentrations of these metal and non-metal ions in theinfluent and effluent (at steady state) of the RAB and BC reactors areshown in FIGS. 25A-25D. Among various ions, sodium and calcium were mostpredominant, followed with sulfur, magnesium, and potassium. For all thewastewaters used, the BC reactors had a limited capability of removingthose ions as the influent and effluent concentrations of those elementswere almost the same. On the contrary, the RAB reactors demonstratedcertain ion removal capacities. The RAB reactors at 3-day HRT (RAB-3)removed more ions than those at 1-day HRT (RAB-1). When industrial WWwith high TDS was used as the influent, RAB reactor removed about 50%(3-day HRT) and about 30% (1-day HRT) of these five ions from theinfluent, while only about 2% of TDS was removed from the BC reactors(FIG. 25B). The industrial WW with high TDS (FIG. 25B) also led to thehighest removal efficiency of the ions compared to other threewastewaters (FIGS. 25A, 25C, and 25D).

The algae cultured in the RAB reactors demonstrated a high performanceof removing these metals and non-metal ions, especially for theindustrial WW with high TDS. This is probably due to the multipleremoval mechanisms such as bio-assimilation and/or the physicaladsorption by biofilm based EPS.

Ion and EPS Contents of Algal Biomass. The biomass harvested from thealgal reactors was analyzed for its ion content. Table 6 shows the ioncontents of algal biomass (ash-containing) produced from the RAB reactorat 1-day HRT (RAB-1), the RAB reactor at 3-day HRT (RAB-3), and thebubble column at 3-day HRT (BC-3) fed with different wastewater sources.

TABLE 6 Algal Reactor-HRT Compositions RAB-1 RAB-3 BC-3 Low-TDSIndustrial WW Sodium (%) 0.98 ± 0.23 0.77 ± 0.28 0.68 ± 0.27 Potassium(%) 0.68 ± 0.05 0.70 ± 0.02 0.74 ± 0.05 Calcium (%) 6.60 ± 0.87 5.34 ±0.07 5.65 ± 0.95 Magnesium (%) 1.34 ± 0.33 0.86 ± 0.00 2.37 ± 0.55Sulfur (%) 1.48 ± 0.86 0.88 ± 0.17 0.74 ± 0.05 High-TDS Industrial WWSodium (%) 2.56 ± 0.16 2.43 ± 0.04 1.61 ± 0.04 Potassium (%) 0.60 ± 0.120.72 ± 0.01 0.68 ± 0.00 Calcium (%) 13.54 ± 2.82  12.35 ± 0.59  9.90 ±0.36 Magnesium (%) 3.08 ± 0.25 2.02 ± 0.25 7.33 ± 0.20 Sulfur (%) 5.81 ±0.30 4.57 ± 0.17 0.48 ± 0.00 Ames WW Sodium (%) 0.26 ± 0.05 0.26 ± 0.010.15 ± 0.03 Potassium (%) 0.69 ± 0.08 0.68 ± 0.08 0.70 ± 0.24 Calcium(%) 3.67 ± 0.00 3.76 ± 0.00 5.38 ± 1.07 Magnesium (%) 0.43 ± 0.10 0.38 ±0.15 0.45 ± 0.11 Sulfur (%) 0.75 ± 0.05 0.72 ± 0.07 0.84 ± 0.07 AmesWW + NaCl Sodium (%) 1.06 ± 0.25 0.79 ± 0.06 0.73 ± 0.09 Potassium (%)0.67 ± 0.10 0.75 ± 0.04 0.77 ± 0.00 Calcium (%) 6.92 ± 0.00 4.41 ± 0.005.72 ± 0.09 Magnesium (%) 0.31 ± 0.10 0.51 ± 0.20 0.31 ± 0.00 Sulfur (%)0.69 ± 0.02 0.64 ± 0.02 1.15 ± 0.08

Calcium was the most predominant ion in the biomass followed withsulfur, magnesium, sodium, and potassium. Potassium content in biomassmaintained at a relatively constant level (e.g., 0.6 to 0.7%) throughoutall the experimental conditions, while calcium, magnesium, sodium andsulfur contents were altered and matched with the concentration level ofthese ions in wastewaters. The stable potassium content across differentbiomass samples indicated algal cells may have the capability ofadjusting potassium adsorption to maintain a balanced intracellular andextracellular osmosis. The results from sulfur removal from differentwastewaters (FIGS. 25A-25D) indicate that biofilm algae in the RABreactors can absorb more sulfur than the suspended algae in the BCreactors.

In algal biofilm reactors, microalgae cells excrete EPS into theirimmediate environment to form a hydrated biofilm matrix, which wasbelieved to help to adsorb TDS from wastewater; therefore, the algalbiomass was further characterized for the EPS content of the algalbiomass. Polysaccharides and proteins are two major components in algalEPS. Table 7 shows the EPS contents of algal biomass (ash-free dryweight (AFDW)) produced from RAB at 1-day HRT (RAB-1), RAB at 3-day HRT(RAB-3), and bubble column at 3-day HRT (BC-3) fed with differentwastewater sources.

TABLE 7 EPS contents Algal Reactor-HRT (mg/g AFDW) RAB-1 RAB-3 BC-3Low-TDS Industrial WW Protein in EPS  3.28 ± 0.20  2.56 ± 0.14  5.15 ±0.17 Polysaccharide in EPS 95.09 ± 3.51 156.23 ± 10.02 17.56 ± 5.40Total EPS 98.37 158.79 22.71 High-TDS Industrial WW Protein in EPS  8.51± 0.26 13.48 ± 1.87 13.05 ± 1.93 Polysaccharide in EPS 53.72 ± 6.1171.28 ± 7.36 50.94 ± 1.67 Total EPS 62.23 84.76 63.99 Ames WW Protein inEPS 18.01 ± 2.05 20.84 ± 1.28 23.20 ± 0.84 Polysaccharide in EPS 116.95± 0.63  135.27 ± 4.92  80.99 ± 7.24 Total EPS 134.95 156.11 104.18 AmesWW + NaCl Protein in EPS  7.57 ± 0.71  8.79 ± 1.01  4.92 ± 0.18Polysaccharide in EPS 144.85 ± 1.38  148.24 ± 17.05 75.41 ± 006  TotalEPS 152.41 157.03 80.33

Throughout all the biomass samples, the polysaccharide content was muchhigher than the proteins. The EPS protein contents in RAB and BC biomasswere similar, while the EPS polysaccharide content was higher in RABderived biomass than those in BC biomass. As a result, RAB biomasscontained a higher total EPS than the BC derived biomass. Between thetwo HRT levels in the RAB reactors, the 3-day HRT resulted in a higherEPS polysaccharide than the 3-day HRT. The EPS polysaccharides in theRAB biofilm biomass are considered the major contributor for adsorbingTDS ions.

Overall, the results demonstrate that the RAB reactors can efficientlyremove TDS from wastewater and be used as a sustainable andenvironmentally friendly method for wastewater remediation. Theefficiencies of removing TDS, chloride, and other ions of the RABreactors were higher than those of the suspended algal culture systemand depended on the HRT. The EPS content of the algal biofilm,particularly the protein and polysaccharides in EPS, was higher in RABreactors than in suspended culture systems and was responsible for thehigh TDS removal efficiencies.

Example 2

Studies on TDS removal using a RAB system were conducted at theMetropolitan Water Reclamation District of Greater Chicago's O'BrienWater Reclamation Plant. Two heights of the belts of the RAB system wereused, 6-ft tall and 3-ft tall, against a standard raceway pond as acontrol. The wastewater was a stream of supernatant from gravitythickening of sludge. Ash content of the biomass produced was used as asurrogate for TDS removal, as ash left after combustion of algal biomassconsists of mostly salts (metal ions such as Ca, Mg, Cu, Ni, Zn, Fe, Na,K, etc. and anions such as Cl, SO₄, PO₄, CO₃, etc.). These constituentsare either absorbed in algal cells from the wastewater or are adsorbedon surface of algal cell walls and/or on to the EPS produced by algalcells. Only a small proportion of constituents, such as dissolvedorganic compounds, which are considered a part of TDS, are lost duringcombustion process used to quantify ash content in algal biomass. Theresults are shown in Table 8.

TABLE 8 Control Raceway 3-ft RAB 6-ft RAB Ash content (%) 11.4 ± 3.216.7 ± 2.9 20.8 ± 3.7

The results showed that the ash content of the algal biomass from the6-ft RAB system were greater than the ash content of algal biomass fromthe 3-ft RAB. Further, the ash content of the algal biomass from both ofthe RAB systems were greater than the ash content of the algal biomassfrom the control raceway pond. Thus, the results showed that algalbiofilms growing on RAB system, when moved outside of the water columnand exposed to a gaseous environment, are capable of removing greateramounts of TDS from wastewater than the algae growing in suspension inthe water column as in traditional raceway ponds. These Examples andresults are also discussed in Peng, Juan, et al., “Removal of totaldissolved solids from wastewater using a revolving algal biofilmreactor,” Water Environment Research (2019), which is incorporated byreference herein in its entirety.

In various embodiments disclosed herein, a single component can bereplaced by multiple components and multiple components can be replacedby a single component to perform a given function or functions. Exceptwhere such substitution would not be operative, such substitution iswithin the intended scope of the embodiments.

Some of the figures can include a flow diagram. Although such figurescan include a particular logic flow, it can be appreciated that thelogic flow merely provides an exemplary implementation of the generalfunctionality. Further, the logic flow does not necessarily have to beexecuted in the order presented unless otherwise indicated. In addition,the logic flow can be implemented by a hardware element, a softwareelement executed by a computer, a firmware element embedded in hardware,or any combination thereof.

The foregoing description of embodiments and examples has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or limiting to the forms described. Numerous modificationsare possible in light of the above teachings. Some of thosemodifications have been discussed, and others will be understood bythose skilled in the art. The embodiments were chosen and described inorder to best illustrate principles of various embodiments as are suitedto particular uses contemplated. The scope is, of course, not limited tothe examples set forth herein, but can be employed in any number ofapplications and equivalent devices by those of ordinary skill in theart. Rather it is hereby intended the scope of the invention to bedefined by the claims appended hereto.

We claim:
 1. A method of reducing total dissolved solids in wastewatercomprising: providing an algal biofilm, the algal biofilm comprising amaterial configured for the growth and attachment of a defined mass ofalgae; providing a fluid reservoir containing a portion of wastewaterfluid; moving the algal biofilm through the portion of wastewater fluidin the fluid reservoir; providing a stressor to algae in the algalbiofilm to trigger a defense mechanism of the defined mass of algae suchthat a first amount of an extracellular polymeric substance is produced,wherein the stressor comprises exposing the algal biofilm to a firstliquid phase and a second gas phase, and wherein the second gas phasecomprises rotating the algal biofilm out of the first liquid phase toexpose the algal biofilm to ambient air; and removing a portion of totaldissolved solids in the portion of wastewater fluid with theextracellular polymeric substance.
 2. The method of claim 1, wherein thestressor is biotic or abiotic.
 3. The method of claim 1, wherein thestressor is selected from the group consisting of increasing the pH ofthe algal biofilm, decreasing the pH of the algal biofilm, increasingthe temperature of the algal biofilm, decreasing the temperature of thealgal biofilm, modulating the temperature of the algal biofilm,adjusting an amount of light applied to the algal biofilm, adjusting awavelength of the light applied to the algal biofilm, and combinationsthereof.
 4. The method of claim 1, wherein the extracellular polymericsubstance comprises proteins and polysaccharides.
 5. The method of claim1, further comprising an algal growth system, the algal growth systemcomprising: (a) a vertical reactor configured to retain the algalbiofilm; (b) a shaft, wherein the shaft is associated with and supportsthe algal biofilm; and (c) a drive motor, the drive motor being coupledwith the shaft such that the algal biofilm is selectively actuated. 6.The method of claim 1, further comprising harvesting the algae from thealgal biofilm.
 7. The method of claim 1, further comprisingprecipitating salts from the portion of wastewater fluid in the fluidreservoir, wherein removing a portion of total dissolved solids in theportion of wastewater fluid further comprises removing at least aportion of precipitated salts.
 8. The method of claim 1, furthercomprising providing a second amount of extracellular polymericsubstance created by the defined mass of algae.
 9. The method of claim8, wherein the first amount of extracellular polymeric substance isgreater than the second amount for the defined mass of algae.
 10. Amethod of reducing total dissolved solids in wastewater comprising thesteps of: providing an algal growth system comprising: (a) a verticalreactor comprising; (i) a flexible sheet material, the flexible sheetmaterial being configured to facilitate the growth and attachment ofalgae; (ii) a shaft, wherein the shaft is associated with and supportsthe flexible sheet material; and (iii) a drive motor, the drive motorbeing coupled with the shaft such that the flexible sheet material isselectively actuated; (b) a fluid reservoir, wherein the flexible sheetmaterial is configured to pass through the fluid reservoir duringoperation of the algal growth system, the vertical reactor beingpositioned at least partially within the fluid reservoir; and (c) aportion of wastewater, wherein the portion of wastewater is retainedwithin the fluid reservoir and includes an amount of total dissolvedsolids; rotating the flexible sheet material of the algal growth systemthrough the portion of wastewater retained in the fluid reservoir in afirst liquid phase; rotating the flexible sheet material of the algalgrowth system through a gas in a second gas phase, wherein the secondgas phase comprises rotating the algal biofilm out of the first liquidphase to expose the algal biofilm to ambient air to trigger a defensemechanism of the defined mass of algae such that a first amount of anextracellular polymeric substance is produced; and harvesting the algaefrom the flexible sheet material; and wherein stimulating the productionof the extracellular polymeric substance reduces the amount of totaldissolved solids in the portion of wastewater.
 11. The method of claim10, wherein rotation of the flexible sheet material of the algal growthsystem through the gas is a first stressor, and wherein the methodfurther comprises providing a second stressor.
 12. The method of claim10, further comprising providing a plurality of algal growth systems todecrease the amount of total dissolved solids in a water system.
 13. Themethod of claim 10, further comprising precipitating salts from theportion of wastewater fluid in the fluid reservoir, wherein removing aportion of total dissolved solids in the portion of wastewater fluidfurther comprises removing at least a portion of precipitated salts. 14.A method of reducing total dissolved solids in wastewater comprising:providing an algal biofilm, the algal biofilm comprising a materialconfigured for the growth and attachment of a defined mass of algae;providing a fluid reservoir containing a portion of wastewater fluid;moving the algal biofilm including the defined mass of algae through theportion of wastewater fluid in the fluid reservoir; providing a stressorto the defined mass of algae in the algal biofilm to affect the definedmass of algae such that a first amount of extracellular polymericsubstance is created by the defined mass of algae, wherein the stressorcomprises exposing the algal biofilm to a first liquid phase and asecond gas phase, wherein the second gas phase comprises rotating thealgal biofilm out of the first liquid phase to expose the algal biofilmto ambient air; and removing a portion of total dissolved solids in theportion of the wastewater fluid.
 15. The method of claim 14, wherein thestressor is biotic or abiotic.
 16. The method of claim 14, wherein thestressor is selected from the group consisting of increasing the pH ofthe algal biofilm, decreasing the pH of the algal biofilm, increasingthe temperature of the algal biofilm, decreasing the temperature of thealgal biofilm, modulating the temperature of the algal biofilm,adjusting an amount of light applied to the algal biofilm, adjusting awavelength of the light applied to the algal biofilm, and combinationsthereof.
 17. The method of claim 14, wherein the extracellular polymericsubstance comprises proteins and polysaccharides.
 18. The method ofclaim 14, further comprising an algal growth system, the algal growthsystem comprising: (a) a vertical reactor configured to retain the algalbiofilm; (b) a shaft, wherein the shaft is associated with and supportsthe algal biofilm; and (c) a drive motor, the drive motor being coupledwith the shaft such that the algal biofilm is selectively actuated. 19.The method of claim 14, further comprising harvesting the algae from thealgal biofilm.
 20. The method of claim 14, further comprising providinga second amount of extracellular polymeric substance created by thedefined mass of algae, wherein the first amount of extracellularpolymeric substance is greater than the second amount for the definedmass of algae.